Variable stroke hydraulic valve lifter



Jam 1970 R. c. SHUNTA ET AL 3,490,423

VARIABLE STROKE HYDRAULIC VALVE LIFTER Filed June 20, 1968 INVENTORS fiwa/ph Q $711M? Bid/1mm Am/erdz United States Patent US. Cl. 123-90 Claims ABSTRACT OF THE DISCLOSURE A spring returned, cam actuated push rod and rocker mechanism with a variable stroke hydraulic tappet interposed between the push rod and cam, the tappet comprising an upright cup-shaped cylinder member resting on the cam and slidably fitted with two spring-opposed plungers, the upper of which abuts the push rod and the lower of which is carried upwardly with the cylinder member during the cam lift stroke against the biasing force of the spring. The extent to which the upper piston and hence the push rod is raised may be varied by introducing oil at selective pressure into the cylinder member through a side port below the lower plunger, which port is closed by upward movement of the cylinder member. Hydraulic cushioning of the final portion of the return movement of the push rod is effected by a damper piston having a lost motion connection with the upper piston.

Background of the invention This invention relates to variable stroke hydraulic valve lifters or tappets of the type disclosed in our prior US. patent application Ser. No. 653,054, filed July 13, 1967, and now US. Patent No. 3,385,274, and particularly to improvements simplifying the design thereof and improv ing their operation.

In said prior application the outer cylinder member of the tappet was slidably fitted with a cup-shaped inner cylinder member which was, in turn, slidably fitted with a generally cup-shaped plunger whose open end carried a separate seat member for the push rod or other element transmitting the engine valve opening motion of the cam. Also, a second spring was employed to bias the inner cylinder member inwardly of the cam-riding outer cylinder member, and there was no means provided for damping the engine valve closing action during operation of the tapped under less than full-stroke conditions.

Summary of the invention In accordance with the present invention the upper or outermost plunger is slidably fitted directly to the outer cylinder member rather than in the lower plunger, enabling elimination of both the necessity of an extra sliding fit between the parts, as well as the need of a separate push rod seating member. Also, but one spring is employed in the instant tappet, and a damper piston is provided which operates through a lost motion connection with the upper plunger to cushion and silence final closing movements of the engine valve.

Similarly as in the arrangement of our said prior application, the tappet guide has a port connected to a source of hydraulic fluid pressure such as the engine lubricating oil system, and a port is provided in the cylinder member to connect therewith between lift strokes of the tappet. By varying the fluid pressure to these ports the relative height of the inner plunger and hence the length of stroke of the upper plunger and the push rod can be varied. The damping fluid pressure acting on the damper piston can also be supplied as oil from the engine lubricating pump via an upper port in the guide and preferably connected to the ice fluid supply line upstream of the valve which regulates the lift control pressure.

Brief description of the drawing FIGURE 1 shows a portion of an internal combustion engine in transverse section, illustrating application of a tappet embodying the invention, the parts being shown in their relative positions prior to start of cam lift.

FIGURE 2 is an enlarged view of the tappet, in longi tudinal section along line 22 of FIGURE 1, and schematically showing the tappet fluid supply and control means.

FIGURE 3 is a view similar to FIGURE 2 but showing the parts in their relative positions of approximately maximum lift.

Description of preferred embodiment Referring now in detail to the drawing and first to FIG- URE 1, the upper portion of an engine cylinder block 1 is shown, having a cylinder head 2 on which is mounted a rocker 3 for operating a spring closed valve 4 or other reciprocably driven element. The tappet, designated generally by the numeral 5, is reciprocable in guide means formed by a tappet bore 6 in the cylinder head directly above the engine driven cam 7. A push rod 8 interconnects the tappet and the rocker 3. The parts are shown in FIGURE 1 in their relative positions prior to the start of the lift stroke of the cam 7.

As shown in FIGURE 2, the tappet comprises an upwardly open cylinder member 9 having an external annular groove 10 connected by one or more side ports 11 to an internal chamber 12 adjacent its lower end 13. This lower end 13 rests on the cam 7, and the tappet bore 6 which has a fluid supply port 14 which is in registry with the groove 10 during the dwell portion of the cam cycle (i.e. between lift strokes). Supply port 14 is schematically shown connected by conduit means 15 to a source of hydraulic fluid pressure such as the engine lubricating oil pump 16 whose output is normally maintained at a suitable pressure, in the order of 30 to 60 p.s.i., by the usual relief valve 17. Between the pressure source and the supply port 14 is a pressure control valve 18 for varying the fluid pressure in the tappet chamber 12.

Slidably fitting the cylinder member 9 are an inner or lower plunger 19 and an outer or upper plunger 20, between which is provided spring means shown in the form of a coil spring 21 which biases the upper plunger 20 against the push rod and biases the lower plunger downwardly toward the closed end 13 of the tappet cylinder member. A stop, shown in the form of a reduced diameter lower extension 22 of the lower plunger, serves to limit downward movement of this plunger in the cylinder member. When this stop is in abutment with the cylinder closed end 13 and the engine valve 4 is in closed position, the opposing ends 23 and 24 of the plungers are held spaced apart by the spring 21. This spring, however, is yieldable to accommodate abutting engagement between the plungers, and suflicient oil pressure is available through selective adjustment of the control valve 18 to force such abutment of the plungers. One or more drain ports 25 are provided in the sides of the cylinder member 9, together with a connecting annular external groove 26 of suflicient width to provide registry with a drain port 27 in the guide bore 6 throughout the lift stroke of the tappet.

Intermediate its ends the upper plunger 20 is provided with a transverse wall 28 which forms the seat for the push rod 8. Where feed of engine lubricating oil upward through the push rod is to be provided, a central opening 29 is drilled through this wall 28 to communicate with the bottom end aperture 30 in the hollow push rod, and a flow control valve 31 is inserted below the opening 29 within the upper plunger. This valve 31 is shown in the form of a plate whose downward or opening movement is limited by a retainer plate 32 held in place by the upper end of the spring 21. The chamber for the flow control valve may be supplied via a third port 33 in the tappet guide, connecting with a wide external annular groove 34 on the cylinder member 9. This groove, in turn, connects with a wide external'annular groove 35 on the upper plunger via a cylinder member port 36, the plunger groove being connected to the flow valve chamber via a lateral passage 37.

The upper plunger has a portion 38 extending outwardly of the cylinder member 9 and having a lost motion connection with a damper piston 39 which is also slidably supported in the tappet bore 6. The damper piston has an annular bottom wall 40 slidably embracing the sides of the upper piston portion 38 so that the latter may freely move upwardly without imparting upward movement to the damper piston. Downward movement of the upper piston to its position shown, corresponding with the closed position of the engine valve and push rod 8, effects a downward shifting of the damper piston by reason of the overlying engagement of an external flange 41 on the upper plunger with the damper piston wall 40. Upward movement of the damper piston is limited by a stop, shown in the form of a snap ring 42 seated in an internal groove adjacent the upper end of the guide bore 6. An annular damping fluid chamber 43 is thereby formed, whose lower end is defined by an annular wall 44 secured to the guide bore 6 between a shoulder 45 therein and a second snap ring 46. Fluid'supply to the damping chamber 43 is provided through a passage 47 leading into the guide bore from a conduit fitting 48. Within the passage 47 is a check valve ball 49 which is normally held closed against a seat 50 on the fitting 48 by a small spring 51.

During operation, oil from the pump 16 is delivered at the pressure regulated by the relief valve 17 to the conduit 15 which distributes it to the damper chamber 43, lubricant supply port 33 and lifter supply port 14. The pressure reaching the latter port for delivery into the tappet chamber 12 can be controlled with the valve 18 to vary the relative height of the lower lunger 19 in the tappet cylinder during the lift stroke. Thus with a mimimum pressure setting of the control valve 18, the lower plunger is in the bottomed condition shown, such that during the lift stroke of the cam 7 the upper plunger, push rod and. engine valve remain stationary in their valve-closed position and the spring 21 is merely compressed as the lower plunger moves upwardly toward the upper plunger. With increased oil pressure delivered to the chamber 12 by a higher setting of the control valve 18, the lower plunger is forced upwardly against the biasing force of the spring 21 so that abutment between the two plungers occurs before maximum lift stroke on the cam develops, and they and the cylinder member 9 thereafter move upwardly as a unit until the cam reaches its maximum lift position. A partial opening only of the engine valve is thus obtained. In the maximum pressure setting of the control valve 18 the lower plunger is elevated to a position of abutment with the upper piston while the cylinder member 9 remains on the base circle of the cam. During the subsequent lift stroke of the cam a certain degree of foreshortening ofthe tappet occurs due to increased pressure developing in the chamber 12, which pressure may exceed that of the supply pressure key set by the valve 18. However, as the cylinder member rises in the guide bore 6 during the initial portion of the cam lift stroke the cylinder port 11 and groove move out of registry with the supply port 14, trapping the oil remaining in the chamber 12, and both the lower plunger 19 and upper plunger 20 thereafter move upwardly in unison with the cylinder member 9.

FIGURE 3 shows the parts in their maximum lift positions.

The damper piston 39 is at all times urged upwardly by the oil pressure in the damper chamber 43, and during upward travel of the upper plunger 38 this damper piston is thus held against its stop 42. During the return stroke of the upper piston it slides downwardly through the annular wall 40 of the damper piston until the upper piston flange 41 comes into abutment with the amper piston wall 40. The height of the stop ring 42 is selected such that the extent of downward travel of the damper piston is adequate, in conjunction with the closeness of its sliding fits with the guide bore 6 and the piston portion 38, and the sliding fit of the fixed wall 44 with the latter to provide sufficient cushioning action to silence the final closing of the engine valve.

Neither the action of the damper piston nor variation of the tappets effective lift stroke through adjustment of the control valve 18 interferes with the flow of lubricating oil into the upper plunger passage 37 for the overhead oil feed up through the push rod, since the upper plunger groove 35 and the cylinder member groove 34 are both made wide enough to maintain registry with cylinder member port 36 and guide port 33, respectively, throughout their range of movement. The rate of such overhead oil feed is accordingly dependent only on the well-known metering action of the flow control valve 31.

It will be appreciated that various changes in the design and arrangement of the parts may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. The combination of a hydraulic tappet comprising a cylinder member closed at one end, inner and outer plungers slidably fitting the cylinder member for reciprocable movement therein relative to each other and to said closed end, spring means acting between the plungers to urge the inner plunger toward said closed end and the outer plunger in the opposite direction, said spring means normally spacing the plungers from each other but being yieldable in response to a predetermined force opposing movement of the outer plunger in said opposite direction to accommodate movement of the inner plunger into abutment with the outer plunger, and means for introducing hydraulic fluid under pressure to the interior of the cylinder member between said closed end and the inner plunger, said last named means including guide means slidably supporting the cylinder member for longitudinal reciprocation and having a fluid supply port closable by the the cylinder member, and a side port in the cylinder member registrable with said supply port only between lift strokes of the tappet.

2. The combination of claim 1, together with stop means on one of said closed end and inner plunger for engagement with the other in preventing closure of said side port during relative movement of the inner plunger and said closed end toward each other.

3. The combination of claim 2, together with a damper plunger having a lost-motion connection with the outer plunger, a fixed wall opposite the damper piston, means including a check valve for introducing fluid under pressure between said wall and damper piston and a stop limiting movement of the damper piston in the direction away from said wall, said lost motion connection freely accommodating movement of the outer plunger in said opposite direction but operative to interconnect the damper and outer plungers for movement of the damper piston away from said stop prior to the outer plunger fully completing its return movement.

4. The combination of claim 3, wherein said outer plunger has a portion extending outwardly of the cylinder member and both said damper piston and wall slidably embrace said outer plunger portion, said guide means fixedly supporting said wall and slidably supporting the damper piston.

5. The combination of claim 3, including a source of hydraulic fluid pressure connected to the upstream side of said check valve, conduit means connecting said source to said supply port, and means for controlling the fluid pressure in said conduit means between said source and said supply port.

References Cited UNITED STATES PATENTS Meinecke. Heiss.

Van Slooten. Williams. Voorhies. Shunta et al. Donnelly et al.

FOREIGN PATENTS 3/1950 Canada.

AL LAWRENCE SMITH, Primary Examiner 

